Permanent magnet eddy brake with flux-steering poles

ABSTRACT

Eddy current braking apparatus includes an array of spaced apart permanent magnets and a plurality of flux steering magnets may be disposed in gaps between the spaced apart permanent magnets. The flux steering magnets are orientated in a manner to provide a steering flux polarity that is rotated about 90 with respect to a polarity magnet flux of the spaced apart permanent magnets in order to increase the flux density in the air gap which results in better performance of the brake. Alternatively, cubic magnets may be used with each magnet being arranged to provide a change in flux polarity between adjoining magnets. An electrically conductive member is provided for engaging the magnetic flux provided by the array of permanent magnets and the magnets and conductive member are mounted for enabling relative motion between the magnet and the conductive member to produce eddy currents in the conductive member and resulting in a braking force between the magnets and the conductive member.

The present invention is a continuation-in-part of U.S. Ser. No.09/504,575 filed Feb. 15, 2000.

The present invention is generally related to permanent magnet linearbrakes and is more particularly directed to eddy brake systems formovable cars, for example, rail supported cars, go-carts, elevator cars,conveyor cars, and roller coaster cars, among others.

As a specific example, the majority of hereinbefore constructedentertainment rides, such as roller coasters, have relied on frictionbrakes for deceleration and stopping of wheel-mounted cars. However, dueto friction, such brakes are subject to wear and must be regularlymonitored and serviced to maintain proper operating conditions.

Linear eddy current brakes would be a preferable replacement for suchfriction brakes inasmuch as no contact is made with the rail for brakingand consequently, they are free from wear due to friction. Eddy currentbrakes are based on the law of induction. When a conductive member ismoved through a magnetic field, eddy currents are generated in themember and a secondary magnetic field caused by the eddy currents isopposed to the magnetic field through which the member passes. Theresulting force component acts opposite to the traveling direction ofthe member.

Electromagnetic coils may be utilized to generate the magnetic field forinducing eddy currents in the moving member, however, suchelectromagnetic systems require elaborate controllers in order to excitethe coils at a proper time to effect the braking. Accordingly, it ismore preferable to effect eddy current braking through the use ofpermanent magnets.

Hereinbefore mentioned, a permanent magnetic linear eddy current brakesystems has utilized two arrays from magnets attached to stationaryrails with a conducting fin disposed on a moving object and arranged topass through a gap provided between the two arrays of magnets. As thefin is passed through the magnet arrays, an electric eddy current isinduced therein which reverses as the fin passes from a magnet of onepolarity to a magnet of opposite polarity. As hereinabove noted, a forceis then created and exerted on the fin which causes a braking force.Other prior art devices include Free Fall Towers which utilize twoarrays of magnets on a car which travels along a stationary fin.

The hereinbefore linear braking systems have utilized two arrays ofpermanent magnets spaced apart from one another to establish a channelor gap there between the passage of a fin. This structural limitationlimits such braking systems to applications on linear, or straight railsections. Accordingly, there is a need for an eddy current brakingsystems which can be utilized on curvilinear rail sections and further,it is desirable to utilize a single array of permanent magnets in aneddy current braking system in order to reduce the cost thereof.

SUMMARY OF THE INVENTION

Eddy current braking apparatus, in accordance with the presentinvention, generally includes a single array of permanent magnets whichprovides a magnetic flux and a plurality of flux steering magnetsdisposed in gaps between said spaced apart permanent magnets. The fluxsteering magnets are oriented in a manner to provide a steering fluxpolarity that is rotated about 90° with respect to a polarity of themagnetic flux of said spaced apart permanent magnets. An electricallyconductive means is utilized for exclusively engaging the magnetic fluxprovided by the single array of permanent magnets.

Means are provided, mounting the magnets and the conductive means, forenabling relative motion between the magnets and the conductive means inorder to produce eddy currents in the conductive means which result in abraking force between the magnets and the conductive means.

More particularly, the present invention may include a car with themagnets disposed on the car and the conductive means being stationary.In this instance, the conductive means is not limited to a linearconfiguration but may, in fact, be disposed in a curvilinearrelationship. The car in this instance is guided along the appropriatecurvilinear path.

Alternatively, the present invention may provide for the conductivemeans to be disposed in the car and the array of permanent magnets in astationary position. In this instance, the array of permanent magnetsmay be disposed in a curvilinear arrangement with an appropriate guidingof the car along the curvilinear path.

In another embodiment of the present invention, eddy current brakingapparatus for a guided car is provided which includes first magnet meansfor providing a magnet flux with the first magnet means consisting of afirst single array of permanent magnets and a plurality of first fluxsteering magnets disposed in gaps between said first spaced apartpermanent magnets. The first flux steering magnets are oriented in amanner to provide a steering flux polarity that is rotated about 90°with respect to a polarity of the magnetic flux of said spaced apartfirst permanent magnets. A first electrically-conductive means isprovided for exclusively engaging the magnetic flux provided by thefirst array of permanent magnets.

First means, mounting the first magnetic means and the first conductivemeans is provided for enabling relative motion between the firstmagnetic means and the first conductive means in order to produce eddycurrents in the first conductive means resulting in a braking forcebetween the first magnet means and the second conductive means.

Further second magnetic means are provided for producing a magnetic fluxwith the second magnet means consisting of a second single array ofpermanent magnets and a plurality of second flux steering magnetsdisposed in gaps between said second spaced apart permanent magnets. Thesecond flux steering magnets are oriented in a manner to provide asteering flux polarity that is rotated about 90° with respect to apolarity of the magnetic flux of said spaced apart second permanentmagnets. A corresponding second, electrically conductive means isprovided for exclusively engaging the second magnetic flux provided bythe second single array permanent magnets.

Second means, mounting second magnet means and the second conductivemeans, is provided for enabling relative motion between the secondmagnet means and the second conductive means in order to produce eddycurrents in the second conductive means resulting in a breaking forcebetween the second magnet means and the second conductive means.

In one embodiment, the first and second magnet means may be disposed onopposite sides of the car and in another embodiment, the first andsecond conducted means are mounted on opposite sides of the guided car.

In yet another embodiment of the present invention, cubic permanentmagnets may be utilized in a way with each permanent magnet beingoriented with a flux polarity that is rotated about 45° or about 90°with respect to a flux polarity of an adjoining, or adjacent, permanentmagnet. This special orientation of rotating magnetization vectorsforces the magnetic field on one side of the magnet array which resultsin a significantly higher braking force than a standard array withoutback iron.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and features of the present invention will be betterunderstood by the following description when considered in conjunctionwith the accompanied drawings in which:

FIG. 1 is a representation of the prior art illustrating a car with adepending fin passing through a cap between two stationary arrays ofpermanent magnets;

FIG. 2 is a representation of one embodiment of the present inventiongenerally showing a single array of permanent magnets attached to a carand disposed for movement past a stationary electrically conductivemember;

FIG. 3 is a representation of another embodiment of the presentinvention similar to that shown in FIG. 2 in which the single array ofpermanent magnets is stationary and the electrically conductive memberis attached to a car;

FIG. 4 is a plan view representation of the embodiment shown in FIG. 2or 3, illustrating a curvilinear pattern of permanent magnets orconductive members;

FIG. 5 is yet another embodiment of the present invention similar toFIGS. 2 and 3 and utilizing a Halbach permanent magnet arrangement;

FIG. 6 is a representation of yet another embodiment of the presentinvention utilizing two arrays of permanent magnets each attached toopposite sides of a car, along with associated stationaryelectrically-conductive members;

FIG. 7 is a representation of yet another embodiment of the presentinvention similar to that shown in FIG. 6 with the two arrays ofpermanent magnets being attached directly to the car without the use ofback iron which is achieved through a specific arrangement of thepermanent magnets known as a Halbach arrangement;

FIG. 8 is a plan view representation similar to that shown in FIG. 4,illustrating a curvilinear arrangement enabled by the configuration ofnew embodiment shown in FIGS. 6 and 7;

FIG. 9 is a representation of a prior art arrangement of permanentmagnets;

FIG. 10 is a representation of an arrangement of permanent magnets inaccordance with the present invention with flux steering magnetsdisposed between the permanent magnets;

FIG. 11 is a representation of an array of cubic permanent magnets inaccordance with the present invention with the magnet flux polaritybetween adjoining magnets being about 90°; and

FIG. 12 is a representation of an array of cubic permanent magnets inaccordance with the present invention with the magnet flux rotatedbetween adjoining magnets being about 45°.

DETAILED DESCRIPTION

With reference to FIG. 1, there is shown a representation 10 of priorart linear eddy current braking system which includes a conductivemember, or fin, 12 fixed to an underside 14 of the car between wheels 20which are supported by rails 22.

The prior system 10 is configured and arranged for causing the fin 12 topass between two arrays 26, 28 of permanent magnets which abut aferromagnetic back iron 30, 32 as is well known in the art. The magnetarrays 26, 28 and back irons 30, 32 are stationary and affixed tostructure not shown in FIG. 1. Magnetic flux maintained in a gap 36between the two magnet arrays 26, 28 is intercepted by the electricallyconductive fin 12 for producing eddy currents therein and a brakingforce as is well known in the art.

Numerous variables affect the braking force in eddy current orelectrodynamic braking as is well known in the art. These variablesinclude:

B, magnetic flux density B, magnetic flux density a higher flux densityresults in a higher braking force with the braking force scaling as B3.The flux density at the conducting member depends on permanent magnetstrength, integrity of the magnetic circuit, and airgap length A, totalmagnet area Braking force is proportional to B³ A,. Hence a higher areaof permanent magnets material results in proportionally higher brakingforce. g, airgap Airgap affects magnitude of the flux density. Ingeneral, operation at a smaller airgap g results in a higher magneticflux density B and hence a higher braking force. ν, relative velocitybetween For a given magnet arrangement and permanent magnets and finconducting fin thickness there is an optimum velocity which maximizesthe magnetic braking force. T, conducting fin thickness The conductingfin thickness T, magnetic pole spacing p, and electrical, σ of the finalso affecting the braking force. It is a multi-dimensional optimizationproblem to determine an optimal thickness, pole spacing and electricalconductivity. P, pole pitch (distance between adjacent N and N poles ina magnet array) σ electrical conductivity of conducting fin

Limitations of the prior art devices, such as that shown in FIG. 1 whichutilize two arrays of stationary permanent magnets and a movable fin,include cost because of the number of magnets necessary and further thestructural limitations such as precise alignment of the arrays 26, 28 toform the narrow gap 36 through which the fin 12 must pass. It should beapparent that this prior art configuration would not be suitable forimplementation along a curvilinear track, not shown in FIG. 1,supporting the car wheels 20.

The present invention is represented by the embodiment 40 shown in FIG.2, includes a single array 42 of permanent magnets fixed to a car 44with a back iron 46 disposed therebetween. Similar to the prior art 10,the car 40 may be supported by rails 48 and moveable therealong bywheels 50. It should be appreciated that while a rail guided care isshown in the Figure, the present invention is not limited thereto but isapplicable to non-guided objects as well.

The single array 42 of permanent magnets is a means for providing amagnetic flux. An electrically conductive member 54 provides a means forexclusively engaging the magnetic flux provided by the single permanentmagnet array 42. To enhance its effectiveness, the member 54 may besupported by the back iron 56 which is ferromagnetic and affixed tostationary supporting structure or ground 60.

The rails 48, wheels 50, and the ground in combination, provide a means,mounting the magnet array 42 and conductive member 54, for enablingrelative motion between the magnet array 42 and the conductive member 54to produce eddy currents in the conductive member 54 which results in abraking force between the magnet array 42 and the conductive member 54.

The size and number of the magnets in the array 42 as well as the sizeand configuration of the conductive member 54 and the back irons 46 56and a gap 62 that between are configured for providing the requiredbraking force and calculated in accordance with the variables heretoforeset forth.

Turning now to FIG. 3, there is shown another embodiment 66 of thepresent invention with common reference numerals representing identicalor substantially the same components as those shown in FIG. 2. In thisembodiment 66, a conductive member 70 is coupled to the car 44, througha back iron 72 and an array 74 of permanent magnets is attached to thesupporting structure 60 through a back iron 76. Principal operation ofthe embodiment 66 is identical to that of the embodiment 40 shown inFIG. 2.

Importantly, the embodiments 40, 66 in accordance with the presentinvention enable braking of the car 44 over curvilinear sections oftrack 48 as represented in FIG. 4. While the curvilinear relationship inthe Figure is shown in two dimensions, three dimensional curvilinearrail or track may also be used in accordance with the present invention.Thus, curvilinear in the context of the present invention meanscurvature in two or three dimensions in this instance, the conductivemember 54 is comprised of a plurality of the segments 54A centeredbetween the curvilinear rails 48. It should be appreciated that whileFIG. 4 shows the embodiment shown in FIG. 2 with the conductive members54 being stationary in this configuration is also obtainable with theembodiment 66 in which the permanent magnets 74 are stationary anddisposed between the rails 48.

Yet another embodiment 80 of the present invention is represented inFIG. 5 with common character references representing identical orsubstantially the same components as the embodiment 40 shown in FIG. 2.In the embodiment 80, a Halbach array 82 of permanent magnets isutilized. This arrangement of permanent magnets provides a greater fluxon one side 84 of the array 82, than another side 86 which eliminatesthe necessity for any back iron such as with the standard array shown inFIG. 2. This permanent magnet array is well known, see “Design ofPermanent Multiple Magnets with oriented rare earth cobalt material”. KHalbach; Nuclear Instruments & Methods, Vol. 169, 180 pp. 110.

It should also be appreciated that the ferromagnetic backing 56, 72 ofthe embodiments 40, 66 and 80, because of the magnetic coupling to themagnet array 42, 74 respectively, provides a means creating a holdingforce between the magnets 42, 84, the attached car and the back iron 56.

Thus, after a moving car is stopped by the braking system, it can beheld in place in a stopped position. This feature is not feasible withthe prior art system shown in FIG. 1.

Turning now to FIG. 6, there is shown another embodiment 90 in thepresent invention with character references shown in FIG. 6,representing identical or substantially similar components herein beforediscussed. The embodiment 90 includes two arrays 92, 94 of permanentmagnets disposed on opposite sides 94, 46 of the car 44 and coupledthereto through back irons 100, 102.

Conductive members 104, 106 are affixed in the structure 108, 110through back irons 112, 114. The principle of operation in the sizing ofthe magnets 92, 94 conductive members 104, 106 and back irons 112, 114are in accordance with the principles herein above set forth.

Yet another embodiment 120 is shown in FIG. 7 with identical characterreferences representing identical or substantially similar components asherein before discussed. The embodiment 120 utilized Halbach permanentmagnet arrangements 122,124 attached to the opposite sides 94,96 of thecar 44, which eliminates the need for back iron. This aspect of theembodiment 120 is substantially the same as that described in FIG. 5,embodiment 80.

Conductive members 130, 132 attached through back irons 134, 136 tosupport the structure 108, 110 as hereinabove described.

The embodiment shown in FIG. 7 also enables the use of curvilinear rails48 as represented in FIG. 8 with identical character referencesrepresenting identical or substantially similar components as shown inFIG. 6.

It should be appreciated that it is important to maximize the force perpound of permanent magnets 42, 72, 84, 122, 124 required. Thisimportance is derived from the fact that in a permanent magnet brake,the material cost of the permanent magnet material is a large fractionof the total system cost Accordingly, the present invention provides forimproving the braking forces in order to minimize the total system cost.

For instruction purposes, a prior art permanent magnet array 150 isshown in FIG. 9 as part of a prior art braking system 152. In thissystem the array 150 of spaced apart magnets 154, 156, 158 are fixed toa back iron 160 in a spaced apart relationship with gaps 162, 164therebetween. FIG. 9 is a representation only and only three magnets154, 156, 158 are shown for explanatory purposes. Also represented is anelectrically conductive means, or member 170 for engaging a magnet flux(not specifically indicated) provided by the single array 152 ofpermanent magnets 154, 156, 158.

With reference now to FIG. 10 there is shown in representation form abraking system 176 which includes a magnet array 178 including magnets180, 182, 184 along with a conductive means or member 186.

In accordance with the present invention, a plurality of flux steeringmagnets 190, 192, 194, 196, 198, 200 are provided and disposed in gaps202, 204, 206, 208 between the spaced apart permanent magnets 180, 182,184. Again, FIG. 10 shows only 3 permanent magnets 180, 182, 184 forrepresentation purposes.

Importantly, the flux steering magnets 190, 192, 194, 196, 198, 200 areoriented in order to provide a steering flux polarity indicated by thearrows 220, 222, 224, 226, 228, 230 that is rotated about 90 withrespect to a polarity, indicated by the arrows 240, 242, 246 of themagnetic flux of the spaced apart permanent magnets 180, 182, 184.

Placement of the flux steering magnets 190, 192, 194, 196, 198, 200increases the flux density in the gaps 202, 204, 206, 208. This resultsin a higher force per unit pound of permanent magnet 180, 182, 184 aswell as a higher force per unit length of the brake system 176.Accordingly, the use of the flux steering magnets 190, 192, 194, 196,198, 200 results in increased system 176 performance and lower system176 cost.

Another advantage of the flux steering magnets 190, 192, 194, 196, 200is the fact that less flux on the top side 250 the array 176 requiresless back iron 256, for a given amount of braking force. This is ofimportance with total system weight means to be minimized.

Further improvement may be obtained through the use of cubic magnets 270in array 272 as shown in FIG. 11 along with a reaction rail, orconductive member, 274. The use of cubic magnets 270 facilitatesmanufacture since only one type of magnet 270 is required, i.e., themagnets 270 are cubic and identical.

Still further improvement is obtained by assembling an array 278 ofmagnets 280-294 as shown in FIG. 12 along with a conductive member 296.The magnets 280-294 are cubic but have magnetization at a 45° angle withrespect to adjacent magnets 280-294 as shown by the polarization arrays300-314. As shown, there are 8 magnets 280-294 in the array 278. This isto be contrasted with the array 272 shown in FIG. 11 which includes fourmagnets 270A, 270B, 270C, 270D in the array 272.

It should be appreciated that multiple arrays 272 or 296 may be utilizedin combination with one another. The rotating magnet arrays 272, 296 maybe simply manufactured by sliding the cubic magnets 272, 280-294 intolong thin-walled tubes (not shown). The resulting array 272, 296 isself-supporting and may be mounted either to a wayside (not shown) or toa moving vehicle (not shown).

Because the arrays 272, 275 do not use back iron, they are lighter thanstandard arrays 26, 28 as shown in FIG. 1. In addition, the arrays 272,278 are self-shielding, hence there is very little strong magnetic fieldoutside of the array 272, 278. This self shielding is accomplishedwithout back iron.

It should be further appreciated that in FIG. 11, there is shown fourmagnets 270 in the array 272 and in FIG. 12 eight magnets 280-294 in thearray 278. Other members of magnets (not shown) may be used in an array(not shown), such as 9 or 10, for example with appropriate magnetic fluxorientation.

Although there has been hereinabove described Eddy current brakingApparatus in accordance with the present invention for the purpose ofillustrating the manner in which the invention may be used to advantage,it will be appreciated that the invention is not limited thereto.Accordingly, all modifications, variation or equivalent arrangementswhich may occur those skilled in the art should be considered to bewithin the scope of the invention as defined in the appended claims.

What is claimed is:
 1. Eddy current braking apparatus comprising: magnet means for providing a magnetic flux, said magnet means consisting of a single array of permanent magnets and a plurality of flux steering magnets disposed in gaps between said spaced apart permanent magnets, said flux steering magnets being oriented in order to provide a steering flux polarity that is rotated about 90° with respect to a polarity of the magnetic flux of spaced apart permanent magnets; electrically conductive means for exclusively engaging the magnet flux provided by the single array of permanent magnets; means, mounting the magnet means and conductive means, for the enabling relative motion between the magnet means and conductive means to produce eddy currents in the conductive means resulting in a braking force between the magnet means and the conductive means; and ferromagnetic backing means, supporting the conductive means, for providing a holding force between the magnetic means and the conductive means.
 2. The apparatus according to claim 1 where said flux steering magnets are smaller that the permanent magnets.
 3. The apparatus according to claim 2 wherein at least two flux steering magnets are disposed in the gap between permanent magnets.
 4. The apparatus according to claim 3 wherein each flux steering magnets is less than half the size of each of the permanent magnets.
 5. The apparatus according to claim 4 wherein each two flux steering magnets disposed between permanent magnets have flux polarization 180 degrees to one another.
 6. The apparatus according to claim 5 wherein all of the steering magnets and permanent magnets are of approximately equal thickness.
 7. Eddy current braking apparatus comprising: a car moveable along at least one rail; magnet means, disposed on the car for providing a magnetic flux; conductive means disposed in a curvilinear pattern exterior to the car, for engaging the magnetic flux and causing movement of the car along the rail to produce eddy currents in the conductive means resulting in a braking force between the magnet mean and the conductive means; and ferromagnetic backing means, supporting the conductive means, for providing a holding force between the magnetic means and the conductive means.
 8. The apparatus according to claim 7 wherein the magnet means comprises an array of permanent magnets and a plurality of flux steering magnets disposed in gaps between said spaced apart permanent magnets, said flux steering magnets being oriented in order to provide a steering flux polarity that is rotated about 90° with respect to a polarity of the magnetic flux of spaced apart permanent magnets.
 9. Eddy current braking apparatus comprising: a car moveable along at least one rail; magnet means, disposed in a curvilinear pattern exterior to the car, for providing a magnetic flux; conductive means, disposed on the car, for engaging the magnetic flux and causing movement of the car along the rail to produce eddy currents in the conductive means resulting in a braking force between the magnet means and the conductive means; and ferromagnetic backing means, supporting the conductive means, for providing a holding force between the magnetic means and the conductive means.
 10. The apparatus according to claim 9 wherein the magnet means comprises an array of permanent magnets and a plurality of flux steering magnets disposed in gaps between said spaced apart permanent magnets, said flux steering magnets being oriented in order to provide a steering flux polarity that is rotated about 90° with respect to a polarity of the magnetic flux of spaced apart permanent magnets.
 11. Eddy current braking apparatus comprising: magnet means for providing a magnetic flux, said magnet means consisting of an array of cubic permanent magnets, each permanent magnet being oriented with a flux polarity that is rotated about 90° with respect to a flux polarity of an adjoining permanent magnet; electrically conductive means for exclusively engaging the magnet flux provided by the array of permanent magnets; means, mounting the magnet means and conductive means, for the enabling relative motion between the magnet means and conductive means to produce eddy currents in the conductive means resulting in a braking force between the magnet means and the conductive means; and ferromagnetic backing means, supporting the conductive means, for providing a holding force between the magnetic means and the conductive means.
 12. The apparatus according to claim 11 further comprising a car with the magnet means being disposed on the car and the conductive means being stationery.
 13. The apparatus according to claim 12 wherein the conductive means is curvilinear.
 14. The apparatus according to claim 11 further comprising a car with the conductive means being disposed on the car and the array of permanent magnets being stationery.
 15. The apparatus according to claim 14 wherein the array of permanent magnets is curvilinear.
 16. Eddy current braking apparatus comprising: magnet means for providing a magnetic flux, said magnet means consisting of an array of cubic permanent magnets each permanent magnet being oriented with a flux polarity that is rotated about 45° with respect to a flux polarity of an adjoining permanent magnet; electrically conductive means for exclusively engaging the magnet flux provided by the array of permanent magnets; means, mounting the magnet means and conductive means, for the enabling relative motion between the magnet means and conductive means to produce eddy currents in the conductive means resulting in a braking force between the magnet means and the conductive means; and ferromagnetic backing means, supporting the conductive means, for providing a holding force between the magnetic means and the conductive means.
 17. The apparatus according to claim 16 further comprising a car with the magnet means being disposed on the car and the conductive means being stationery.
 18. The apparatus according to claim 17 wherein the conductive means is curvilinear.
 19. The apparatus according to claim 16 further comprising a car with the conductive means being disposed on the car and the array of permanent magnets being stationery.
 20. The apparatus according to claim 19 wherein the array of permanent magnets is curvilinear. 